1. Field of the Invention
The present invention relates to a high-conductivity carbon thread usable as a light, conductive element, and, more particularly, to a graphitized carbon thread. The present invention also relates to a process for producing the high-conductivity carbon thread.
2. Related Background Art
Carbon or graphite threads are produced in a method to bake fibers of polyacrylonitrile as referred to as PAN or in a method to melt-spin a coal-originated or a petroleum pitch, to subject the spun fiber to infusible treatment, then to bake it, and, if necessary, further to effect thereon heat treatment at a high temperature or graphitization. The former is called PAN-type carbon fibers and the latter pitch-type fibers. These fibers are generally used for reinforcement. To obtain high elasticity and high strength, as many impurities presenting a hindrance upon the carbonization or the graphitization are removed as possible from the precursor material, i.e., PAN or pitch. However, the thus-produced carbon fibers using such refined precursor materials do not show enough conductivity after the graphitization, for example, approx. 1.times.10.sup.3 S/cm of PAN type carbon fibers and approx. 2.times.10.sup.3 S/cm of pitch-type carbon fibers. It is considered that this low conductivity is due to insufficient spreading of carbon hexagonal network even after the graphitization as a whole, allowing many grain boundaries and defects to still exist.
On the other hand, vapor-phase growth carbon fibers as referred to as VGCF obtained by thermal decomposition of gasified organic compound at a high temperature show high conductivity, but generally have a short fiber length. Therefore, use of VGCF is limited. Among them, VGCF as described in Japanese Unexamined Patent Publication Tokkaisho 57-117622 are relatively long with an average diameter of 10 .mu.m and a length of approx. 20 cm, while presenting satisfactory conductivity of 2.times.10.sup.4 S/cm after the graphitization. It is, however, difficult to use the VGCF as a conductive wire, since the fibers are discontinuous as well as lacking in mass-producibility.